Method and apparatus for driving pretensioned piles



y, 1969 s. D. JOHNSON v 3,

METHOD AND APPARATUS FOR DRIVING PRETENSIONED FILES Filed Nov. 50, 1967Sheet of 2 ill I9 V VI l9 l9 1 I l\ 40 l I20 I20 I4 l4 l4 I70 M I70 1 1/b I? w i II 5 l5 E a a a l5 2 i I i S IZb l6b I llcl I60 I20 [I L I20 1I20 flab ,1! 7 I j 4 v I2 flzc z k 1 I'NVENTOR F|G GLENN D. JOHNSON H ISATTORNEY.

y 1959 v G. D. JOHNSQN 3,443,387

METHOD AND APPARATUS FOR DRIVING. PRETENSIONED FILES Filed Nov; 50, 1967Sheet 3 of 2 FIG. 4 FIG. 5

FIG. 7

FIG. 6

INVENTORI GLENN D. JOHNSON HIS ATTORNEY United States Patent 3,443,387METHOD AND APPARATUS FOR DRIVING PRETENSIONED PILES Glenn D. Johnson,Downey, Calif., assignor to Shell Oil Company, New York, N.Y., acorporation of Delaware Filed Nov. 30, 1967, Ser. No. 686,901 Int. Cl.E02d /14 US. Cl. 6153.7 8 Claims ABSTRACT OF THE DISCLOSURE A thin,hollow shell for a piling is tensioned and stressed a predeterminedamount over a driving mandrel to facilitate driving the shell withoutexcessive damage thereto.

Background of the invention This invention relates to a method andapparatus for driving thin pile shells and more particularly to a methodand apparatus for pretensioning a thin-walled pile shell so that it maybe driven without causing excessive damage thereto.

In the placement of concrete and similar pilings in an earth formationit is often necessary to place thin, hollow shells in the formationprior to formation of the body of the pile. Such thin-walled shells arenecessary, especially in areas where the earth formation is soft orloose and likely to cave into the borehole. It is desirable to use asthin a pile shell as possible because of the great savings in materialwhere a great many piles are used. The use of thin-walled pile shells,however, has been quite limited in the past because of the lack of aneflective method of inserting such shells into the soil formationwithout excessive damage thereto. Thin-walled pile shells have generallybeen driven by means of either a plug which engages the lower end of thepile and is driven downward into the formation, pulling the pile shellwith it, or by means of an internal mandrel which also engages the lowerend of the pile and is driven downward into the formation, pulling thepile shell with it. With the use of either the plug or the mandrel thedriving force is applied primarily to the lower end of the pile shellwhile the resistance force applied by the soil is generally appliedalong the entire length of the pile shell. The movement of the shell isgreatest at the bottom and diminishes toward the top. Under suchconditions the pile shell is deformed or otherwise greatly damaged bybeing stretched or torn apart.

It is therefore an object of the present invention to provide a methodand apparatus for driving thinner-walled pile shells than has heretoforebeen possible.

In accordance 'with the present invention, an elongated driving mandrelhaving a pretensioning clamp means near its upper end is inserted in athin-walled pile shell and the shell stretched thereover.

Bl ief description of the drawing A greater understanding of the presentinvention may be obtained from a reading of the following description inconjunction with the accompanying drawings in which:

FIGURE 1 is an elevational view illustrating the general arrangement ofa drive mandrel in position to be inserted into the central bore of atelescoped, thin-walled pile shell.

FIGURE 2 is an elevational view partially in section illustrating thearrangement of the driving mandrel lowered into the shell assembly withthe shell assembly extending over the drive mandrel.

FIGURE 3 is an elevational view partially in section illustrating thearrangement in the shell assembly in driving condition with the pileshell stretched over the drive mandrel.

3,443,387 Patented May 13, 1969 FIGURE 4 is an elevational viewpartially in section illustrating the clamping and stretching apparatusof the present invention.

FIGURE 5 is an elevational view partially in section illustrating thegripping apparatus of the present invention in engagement with the wallof a thin pile shell.

FIGURE 6 is an elevational view partially in section showing thegripping and stretching apparatus of the present invention in grippingengagement with the end wall of the pile shell and extended to itsuppermost or stretched position.

FIGURE 7 is a side elevation partially in section illustrating the lowerend of a thin-walled corrugated pile shell prepared for driving by theapparatus of the present invention.

Description of preferred embodiments Taking a look now at FIGURE 1,there is shown a driving mandrel 11 which is stepped in sections 11a,11b and 11c which are adapted to engage and drive a telescoping pilesuch as that shown at 12. A pretensioning clamp '13 is suitablyconnected or mounted on the upper end of the driving mandrel. Thedriving mandrel 11, as illustrated, is a step-tapered cylindricaltubular member having a plurality of abutting or drive shoulders 14 and15. The telescoping pile 12 which the illustrated mandrel is adapted todrive is a telescoping pile made up of a plurality of sections 12, 12band 12c which are connected together by means of flanges 16 and 17, asmore fully detailed in FIGURES 2 and 3, or other suitable means. Theupper end of section 12a and 12b comprises an outwardlydirected annularflange member 16 and 17 on the upper end thereof. Each pile section 12band 120 comprises an inwardly-directed annular flange member 16a, 1711'on the lower end thereof to engage the outwardly-directed flange of thenext adjacent section of shell. These flange members 16, 16a and 17, and17a are adapted to abut or engage as shown in FIGURES 2 and 3 so thattension applied to the next upper section of shell will be transmittedto the engaged lower section of shell. The abutting or drive shoulders14 and 15 are adapted to engage the corresponding flange shoulder 17band 16b, respectively, of each shell section.

Each step section 11a, 11b or of the drive mandrel is longer by apredetermined amount than each of the pile sections 12a, 12b or 12c, orat least its corresponding section of the telescoping shell that is tobe driven. This predetermined excessive length of each step section ofthe driving mandrel over its corresponding section of telescoping shellinsures that each section of the shell is stretched and thereforetensioned as the shoulders 17b and 16b of the sections come intoengagement with the corresponding drive shoulder 14 and 15 of thedriving mandrel. Suitable means such as a plate, plug or ring 18 isprovided at the lower end of the lowermost section of the pile shell, asshown in FIGURE 3, for engagement by the lower end of section 11a of thedrive mandrel 11. The drive mandrel and the pretensioned pile shell, asshown in FIGURE 3, is driven to the desired depth in an earth formationby any suitable means such as by a pile-driving hammer or by a sonicoscillator 19. A pile driver of the hammer type is well known and needsno discussion here. A driver of the sonic oscillator type suitable forthe present invention may be of a type generally disclosed in US. PatentNo. 2,975,846. Such sonic oscillators operate by establishinglongitudinal elastic vibrations in the pile shell and the mandrel whichresults in a penetration of the shell and the mandrel into the earthformation.

The clamping and pretensioning apparatus of the present invention ismore clearly illustrated in FIGURES 4-6 The clamping and pretensioningapparatus comprises a cylindrical central body members 20 having acentral throughbore 21 and an annular skirt or flange member 22. Theannular body member 23 is connected, as by threads 20a, to the lower endof the central body member 20 on the outside thereof and has a skirtportion 24 which extends upward and concentrically along the centralbody member 20 in spaced relation thereto to form an annular wedgecontaining pressure chamber 25. An annular clamp wedge actuating piston26 is mounted in sealed relation in pressure chamber 25 and extendsupward along the outer cylindrical surface of the central body member20. The actuating piston 26 has an outwardly sloping cam surface 27around which is circumferentially spaced a plurality of clamp wedges 28,each having a gripping surface 28a formed with teeth or serrations toenhance gripping. The clamp wedges 28 may be held in spaced relationaround and in engagement with the camming surface 27 by means of aplurality of grooves which may be preferably of a dovetailconfiguration. A downwardly-extending annular clamp skirt 29 isconnected by suitable means, such as by studs or bolts 30, to an annularpiston member 31 which is reciprocably mounted in sealed relationship inannular chamber 32. The annular skirt 29 has an annular internalgripping surface 29a which is preferably formed with teeth or otherforms of serrations to gripping of a pile shell. An annular pressurerelease or wedge release pressure chamber 33 is formed between clampwedge actuating piston 26 and central body member 20. Conduit means 34supplies hydraulic fluid to the annular pressure chamber 33. Fluid issupplied to pressure chamber 25 for driving annular piston 26 upward bymeans of pressure fluid from conduit 35. The annular piston 31 is moveddownward by means of fluid under pressure in pressure chamber 32 whichis supplied by conduit member 36. An adjustment collar 37 is threadablymounted by means of threads 29a on the outer surface of clamp skirt 29for adjustment thereon to adjust the pretensioning that is to be appliedto the pile shell member. A prtensioning adjustment scale 38 indicatesthe amount of pretensioning. A lock screw 39 locks the adjustment collarinto place after adjustment to prevent accidental movement thereofduring operation of the device.

The lower limit of travel of the stretching or tensioning assembly ofthe present apparatus is determined by stop shoulder or the engagementof stop shoulder 37a with stop shoulder 22a. The distance of shoulder37:: above shoulder 3111 on piston 31 is adjustable by rotating collar37 and determines the distance of travel of the pretensioning pistonassembly and thus the amount of tensioning that may be applied to a pileshell. The upper limit of travel of the tensioning piston assembly isdetermined by the engagement of shoulder 31a with the lower end of skirtmember 22.

In operation or in carrying out the present invention, a driving mandrelis selected which has the proper dimensions with respect to thedimensions of the thin-walled pile shell which it is desired to drive.As illustrated (FIG- URE l) with respect to the present invention, thedriving mandrel 11 is lowered into the center of a nest of telescopedpile shells 12a, 12b and 120 with the lower end of the driving mandrelengaging the lower end of the lower shell section 11a (FIGURE 3) bymeans of a plate 18, or other engaging means such as, for example, aflange, would be suitable. As shown in the illustration of thetelescoped shell, the telescoped pile shell is pulled up over themandrel (FIGURE 2) such as by aid of a hoist line 40 and upward forengagement by the clamp and tensioning means. The clamping assembly2628-29-30-31 is moved downward to a predetermined lowermost position byincreasing the fluid pressure in chamber 32 and lowering the pressure inchamber 25. This predetermined position is selected by means of collar37, and is determined by the amount of stretch of the pile shell neededto obtain the desired tension. The upper end of the pile shell isinserted between .4 the clamping wedges 28 and clamping skirt 29, asshown in FIGURE 4. The clamp wedge actuating piston 26 is then actuatedby the injection of hydraulic fluid into pressure chamber 25 which movespiston 26 upward, camming clamp wedges 28 outward into engagement withthe shell member 12 as shown in FIGURE 5, clamping the shell memberbetween the wedge members 28 and the clamp skirt 29. Continuedapplication of hydraulic pressure into pressure chamber 25 continues tomove the piston assembly 26 and the clamping assembly 28-29- 30-31upwardly carrying therewith the upper end of the shell member 12. Whenthe pile shell is first brought into position for clamping between thejaws of the clamping assembly, the pile shell will appear as shown inFIGURE 2 with the abutting shoulder 16a standing away from the drivingshoulder 15 of the mandrel. As continued pressure is applied into thepressure chamber 25, the clamping and the tensioning assembly movesupward pulling each successive pile shell abutting or drive shoulderinto engagement with the corresponding abutting or drive shoulder on thedriving mandrel, as shown in FIG- URE 3. With the shell in its stretchedor tensioned position as shown in FIGURE 3, the pile shell and mandrelare raised to be driven to the desired depth in an earth formation.After the shell has been driven to the desired depth in the earthformation, the upward pull on the pile shell is then released or relaxesand the clamping engagement released by lowering the pressure in chamber25 and increasing pressure in chamber 33, thus permitting the drivemandrel to be removed from the center of the pile shell as a slurry ofsolidifiable material such as cement or concrete is pumped downwardthrough the hollow bore of the mandrel, thus filling the shell as themandrel is withdrawn.

Although a tapered telescoping pile has been illustrated in conjunctionwith the explanation of the practice of the present invention, it is tobe understood that the present invention is applicable to the driving oflong nontelescoping tapered piles, single diameter pile shells, andother similar structures as would be apparent from the foregoingillustration. Also, it is apparent that corrugated pile shells may bedriven in accordance with the practice of the present invention, asillustrated in FIGURE 7. As shown in FIGURE 7, the corrugated pile shell41 is provided with abutting means in the lower end thereof such as, forexample, plug member 42, which is connected in any suitable manner suchas by welding into the end of the pile shell member. The plug 42 isadapted to be engaged by the driving mandrel 11 as the pile shell isstretched over the mandrel and driven into the earth formation. Adriving cap 43 may be provided for the lower end of the pile shell tofacilitate penetration thereof.

While the invention has been described with respect to a specificembodiment, it is to be understood that many modifications thereof maybe made without departing from the scope of the invention which is to belimited only by the scope of the appended claims.

I claim as my invention: 1. An apparatus for pretensioning thin pileshells to improve the driving thereof, said apparatus comprisng: anelongated driving mandrel adapted to extend into a pile shell;

shell abutting means carried by the lowermost end of said drivingmandrel for drivingly engaging said pile shell at the lower end thereoffor applying a bias thereto in an axial direction;

tension-applying means operatively carried at the top of said drivingmandrel for applying axial bias to said pile shell to elasticallyelongate said shell a predetermined amount to thereby pretension saidshell; and

clamping means operatively carried by said tension-applying means foroperatively connecting said tensionapplying means to the upper end ofsaid pile shell.

2. The apparatus of claim 1 wherein:

said tensioning means comprises prime mover means.

3. The apparatus of claim 1 wherein:

said clamping means comprises a clamp operatively actuated by said primemover means for gripping the upper end of said pile shell.

4. The apparatus of claim 1 wherein:

said driving mandrel comprises an elongated steptapered membercomprising a plurality of abutting shoulders.

5. The apparatus of claim 2 wherein:

said prime mover means comprises body means;

an annular chamber formed in said body means;

annular piston reciprocably mounted in said chamber;

and

cam means formed on said piston for moving said clamping means intogripping engagement with said pile shell.

6. The apparatus of claim 5 comprising:

adjustable stop means to adjust the limit of travel of said piston.

7. The apparatus of claim 5 comprising:

a pressure chamber formed above said piston for reeeiving pressurizedfluid for moving said piston downward; and

a pressure chamber formed below said piston for receiving {pressurizedfluid for moving said piston upward.

8. In a method of driving thin-walled piles the steps selecting a hollowthin-walled pile adapted for engagement with a driving mandrel;

selecting a driving mandrel having a diameter that is slightly less thanthe internal diameter of said pile and said pile having engaging meansat its lower end for engagement with said mandrel engaging means;

inserting said driving mandrel in the bore of said pile and intoengagement with the interior wall adjacent the lower end thereof;

engaging the upper end of said pile with tension-applying means;

applying tension to said pile to at least partially elastically elongateand thereby tension said pile over substantially its entire length; and

driving said mandrel and said tensioned pile to a predetermined depth inan earth formation.

References Cited UNITED STATES PATENTS 2,959,193 11/1960 Guldenzoph eta1. 138-l72 3,232,638 2/1966 Hollander 2851l4 X 3,327,483 6/1967 Gibbons61-53.7

US. Cl. X.R.

